Validation of an isocratic LC method for determination of quercetin and methylquercetin in topical nanoemulsions

The aim of this study was to validate an isocratic LC method for the quantification of either quercetin (Q) or methylquercetin (MQ) incorporated in topical nanoemulsions. The analyses were performed at room temperature on a reversed-phase C18 column using a mobile phase composed of methanol/water (70:30, v/v) and trifluoracetic acid 0.1% at 0.8 mL min−1. The detection was carried out on a UV detector at 368 or 354 nm for Q and MQ, respectively. The linearity, in the range of 0.15-1.5 μg/mL, presented a determination coefficient (r2) higher than 0.99, calculated by the least square method for both flavonoids. No interferences from the excipients (egg-lecithin or octyldodecanol) were detected. The R.S.D. values for intra- and inter-day precision experiments were lower than 2% for both flavonoids. The recovery ranged from 98.9% to 103.46% for Q and from 98.9% to 102.92% for MQ.